Dosimetry system for strontium-rubidium infusion pump

ABSTRACT

The dosimetry system used with a strontium-rubidium infusion system is a very high speed circuit capable of measuring the radioactive dosage infused into a patient in real time. The dosimetry system is capable of receiving very short duration input pulses generated by a photomultiplier tube in response to the presence of radioactivity.

BACKGROUND OF THE INVENTION

The present invention relates to a dosimetry system. In particular, itrelates to a dosimetry system which can be used in an in-line apparatusused to infuse patients with Rubidium-82.

Current statistics show that approximately one-third of all deaths inthe Unites States are related to coronary artery disease. See, forexample, Pohost, G., McKusick, K., and Strauss, W., "Physiologic Basisand Utility of Myocardial Perfusion Imaging" Proceedings of the SecondInternational Symposium on Radiopharmaceuticals, Society of NuclearMedicine, New York 1979, pp. 465-473, and this fact has promptedextensive research to more efficiently diagnose and manage this disease.Recent advances in radiopharmaceutical development and instrument designhave established myocardial scintigraphy as an important new approachfor evaluating coronary artery disease and myocardial perfusion. See,for example, Pierson, R., Friedman, M., Tansley, W., Castellana, F.,Enlander, D., and Huang, P., "Cardiovascular Nuclear Medicine: AnOverview", Sem. Nucl. Med., 9, 224-240 (1979); Leppo, J., Scheuer, J.,Pohost, G., Freeman, L., and Strauss, H., "The Evaluation of IschemicHeart Disease Thallium-201 with Comments on Radionuclide Angiography";Sem. Nucl. Med., 10, 115-126 (1980); Vogel, R., "Quantitative Aspects ofMyocardial Perfusion Imaging", Sem. Nucl. Med., 10, 146-156 (1980);Chervu, R., "Radiopharmaceuticals in Cardiovascular Nuclear Medicine",Sem. Nucl. Med., 9, 241-256 (1979); and Pitt, B., and Strauss, H.,"Cardiovascular Nuclear Medicine", Sem. Nucl. Med., 7, 3-6 (1977).

Myocardial scintigraphy studies have been performed with severalisotopes of potassium, rubidium, cesium, and thallium (T1-201), althoughthe usefulness of all of these nuclides is limited by their non-optimalphysical properties. In spite of its long half-life and low-gammaenergy, T1-201 is currently the most widely used agent for myocardialimaging. See, for example, Poe, N., "Rationale and Radiopharmaceuticalsfor Myocardial Imaging", Sem. Nucl. Med., 7, 7-14 (1977); Strauss, H.and Pitt, B., "Thallium-201 as a Myocardial Imaging Agent", Sem. Nucl.Med., 7, 49-58 (1977); Botvinick, E., Dunn, R., Hattner, R., and Massie,B., "A Consideration of Factors Affecting the Diagnostic Accuracy ofT1-201 Myocardial Perfusion Scintigraphy in Detecting Coronary ArteryDisease", Sem. Nucl. Med., 10, 157-167 (1980); and Wackers, F.,"Thallium-201 Myocardial Scintigraphy in Acute Myocardial Infarction andIschemia", Sem. Nucl. Med., 10, 127-145 (1980).

In diagnostic procedures in which the heart is involved, it is desirablefor a diagnostician to be able to view a patient's heart. Heretofore,various radioactive materials have been used together with radiologicalprocedures for viewing internal organs of patients. It has beendifficult, however, to view a heart because the radioactive substanceswhich could be used for viewing the heart have had a very longhalf-life. Thus, using them with patients involves an element of dangerand also reduces the number of times that a patient could be infusedwithin any given time period. It would therefore be desirable to have adiagnostic apparatus and procedure which could be used with relativesafety for viewing the heart.

Rubidium-82 is a potassium analog. That means it acts similar topotassium when it is infused into a patient. Thus it builds up at a veryrapid rate, i.e., within seconds, in the patient's heart. Rubidium-82also has the advantage of having a very short half-life, approximately76 seconds. Therefore, it decays after a very short period of timefollowing entry into the body, thereby allowing numerous procedures tobe performed within a relatively short time period in a given patient.Rubidium-82 also has the advantage of being observable using a modifiedgamma camera such as a gamma camera of the type manufactured by SearleRadiographics, Inc., called the PHO Gamma IV. A problem with usingRubidium-82 in a patient involves keeping track of the amount ofradiation infused into the patient. In view of the very short half-lifeof Rubidium-82, it is impractical to measure the radioactivity of aparticular dose and to then infuse it into the patient usingconventional means. An accurate method for measuring the amount ofradiation being infused into the patient would be highly desirable forthis particular application.

The availability of improved instrumentation has stimulated interest inthe use of the positron emitter, Rubidium-82, for myocardial imaging.See for example, Beller, G., and Smith, T., "Radionuclide Techniques inthe Assessment of Myocardial Ischemia and Infarction," Circulation, 53(3, Supp. 1) 123-125 (1976); Budinger, T., Yano, Y., Derenzo, S., etal., "Myocardial Uptake of Rubidium-82 Using Positron EmissionTomography," J., Nucl. Med. 20, 603 (1979); Budinger, T., Yano, Y.,Derenzo, S., et al., "Infarction Sizing and Myocardial PerfusionMeasurements Using Rb-82 and Positron Emission Tomography," Amer. J.Cardiol., 45, 399 (1980). Rubidium-82, an analog of the alkali metalpotassium, is rapidly cleared from the blood and concentrated by themyocardium. The short half-life of the Rubidium-82 (76 sec) offers theunique advantage of permitting repeat perfusion and blood flow studiesin patients whose clinical status is rapidly changing.

Rubidium-82 is produced by the decay of its parent, strontium-82. E. R.Squibb and Sons, Inc. has developed a Rubidium-82 generator and infusionsystem which yields an isotonic saline solution of Rubidium-82 atphysiological pH for rapid administration. In animal experiments, thesafety and myocardial uptake of Rubidium-82 has been demonstrated.Therefore this agent has been selected as a candidate for clinicaltrials.

BRIEF DESCRIPTION OF THE DRAWING

In the Drawing:

FIG. 1 is an overall schematic diagram of the strontium-rubidiuminfusion system used in conjunction with the present invention;

FIG. 2 is a front view of the infusion pump control used with thestrontium-rubidium infusion system;

FIG. 3 is a front view of the dosimetry control used with thestrontium-rubidium infusion system;

FIG. 4 is a graph of radioactivity measured (on the y-axis) by thedosimeter probe versus time (on the x-axis);

FIG. 5 is a perspective view of the dosimetry probe;

FIG. 6 is a schematic diagram of the interface between the dosimetryprobe of FIG. 4 and the dosimetry control circuitry;

FIG. 7 is a schematic diagram of the circuit for the Single ChannelAnalyzer used to convert and shape the raw pulses from the dosimetryprobe of FIG. 4;

FIG. 8 is a schematic diagram of the circuit for the Multiply-Dividecircuit used to carry out the formula which converts pulses from theSingle Channel Analyzer into radioactivity present in front of thedosimetry probe;

FIG. 9 is a schematic diagram of one of the Display Controller circuitsused to interface the switches and the displays to the other circuitry;

FIG. 10 is a schematic diagram of the Dose Rate circuit used to providea display of the amount of radiation present in the eluate;

FIG. 11 is a schematic diagram of the Control Circuit which oversees theoperation of the remainder of the circuitry; and

FIG. 12 is a schematic diagram of a valve driver circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a saline bag 10 is connected, through a bulletnose fitting 12 and a piece of tubing 14, to a T-shaped two-way checkvalve 16 having three arms. A first arm 20 includes a one-way valvewhich permits saline to enter the check valve 16, but does not allow itto exit back into the tubing 14. A second arm 22 includes a check valvewhich permits saline to exit from the check valve 16 into a filter 24through a tube 26, but does not allow it to re-enter the check valve 16from the tube 26. A syringe 18, connected to the check valve 16 fillsfrom the saline bag 10 and pumps out through the tubing 26 into thefilter 24. Saline pumped through the filter 24 enters astrontium-rubidium generator 28 which is of the type described morefully in U.S. patent application Ser. No. 156,285, entitled ⁸² RBGENERATING METHOD AND ELUENT, filed on June 4, 1980 by Rudi D.Neirinckx, et al.

Saline pumped through the strontium-rubidium generator 28 exits thegenerator 28 through tubing 30 containing Rubidium-82. The tubing 30 isconnected to a diverter valve 32 having a first arm 34 which leadsthrough tubing 38, an antibacterial filter 40, and ultimately to waste42. A second arm 35 of the diverter valve 32 is connected through tubing44, an antibacterial filter 48, additional tubing 50, and into aninfusion needle 52. The infusion needle 52 is typically inserted intothe arm 54 of a patient 56.

In the preferred embodiment of the invention, the check valve 16 is adual back check valve of the type made by Beckton Dickenson Inc., andthe antibacterial filters are of the type made by Schleicher & Schull astheir type FP030/3.

In the operation of the device, the amount of radioactivity in thesaline eluted from the strontium-rubidium generator 28 must be measuredas it is introduced into the patient 56. Accordingly, a dosimetry probe58 is placed adjacent to the tubing 30 where it measures theradioactivity of the rubidium-containing saline as it leaves thegenerator 28 and enters the diverter valve 32.

In order to use the infusion system, various procedures must beperformed and controlled. In particular, the syringe 18 must be purgedof air, and filled with saline, and the diverter valve 32 must bepositioned. These operations are contingent upon a number of factorsincluding the total volume to be infused into the patient 56, the totaldosage to be infused into the patient 56, the minimum radioactivitywhich must be present in the tubing 30 before any eluate is infused intothe patient 56, the total volume to be infused (Note: The total volumeeluted may differ from the total volume infused into the patient 56 assome volume is likely to be diverted to waste.

The foregoing parameters may be altered from the front panel of twodifferent controllers shown in FIGS. 2 and 3. These are the infusionpump controller 60 and the dosimetry controller 62, repectively. Theinfusion pump controller 60 controls the mechanical movement of thesyringe's plunger 66 via a stepping motor 64 which is connected to theplunger 66.

In the preferred embodiment of the invention, the syringe 18 is asterile, disposable plastic syringe of the type made by Sherwood Medicaland designated as Part. No. 881-514031. The infusion pump controller 60limits the movement of the syringe plunger 66 based upon optical limitdetectors 68, 70 which limit the fully displaced and fully extendedpositions of the plunger 66, respectively. The volume control functionperformed by the infusion pump controller 60 is accomplished by countingthe number of pulses sent to the stepping motor 64.

With reference to FIG. 2, the front panel of the infusion pumpcontroller 60 is shown. The infusion pump controller 60 includes anon/off power switch 72 which is used to turn on the power to the unit.

A set of thumbwheel switches 74 is used to select the total volume (ml)to be eluted. An LED display 76 shows the total volume (ml) which hasbeen eluted. A momentary contact push-button switch 78 is used to startand to stop the movement of the plunger 66 in the forward (inject)direction.

A set of push-button potentiometers comprise the Flow Rate Control 80which is used to determine the volume per unit time which is infused.The Flow Rate Control 80 sets the pulse rate into the stepping motor 64.An LED 82 lights when the end of travel of the plunger 66, as indicatedby the optical limit detectors 68, 70 is reached. A pair of momentarycontact push-button switches 84, 86 are used to control the purge andrefill functions, respectively, of the syringe 18. Thus, if the purgecontrol switch 84 is pushed, and held, the plunger 66 continues to movein the forward direction until it reaches the forward limit detector 68.Similarly, while the refill control switch 84 is pressed and held, theplunger 66 continues to move toward the rear limit detector 70. Thespeed of movement of the plunger 66 during purge and refill operationsare controlled by adjustable screw-type potentiometers 88, 90,respectively.

The infusion pump controller 60 is comprised of a Superior ElectricCompany STM103 Translator Module which is interfaced to provide signalsrepresentative of flow rate, volume eluted, and injection. It is alsointerfaced to be remotely controlled. A pulse called "INIT" indicatesthat the Translator Module has been powered. The "INIT" pulse is used toreset the displays on the dosimetry module. An "INJECT" signal indicatesthat the pump is injecting. Output pulses, corresponding to 0.1 ml stepsof the syringe 18, are provided. An "End of Elution" signal is used toremotely disable the infusion pump controller 60.

With reference now to FIG. 3, the dosimetry controller 62, is comprisedof a number of LED displays and thumbwheel switch sets. In addition, thedosimetry controller 62 includes an on/off switch 92 for providing powerto the unit.

The first set of thumbwheel switches 94 is used to set the volume (ml)to be infused into the patient 56. The LED display 96, immediately abovethe thumbwheel switches 94, displays the volume of eluate which has beeninfused into the patient 56.

The thumbwheel switches 98 are used to set the total dose (mCi) which isto be infused into the patent 56 and the LED display 100 immediatelyabove the total dose thumbwheel switches 98 displays the total dosewhich has been infused into the patient 56. Similarly, the thumbwheelswitches 102 are used to set the dose rate (mCi/sec.) which is to beused to determine when to switch the diverter valve 32 from the wasteposition to the patient 56 position. The actual dose rate which ispresent in the eluate within the tube 30 in front of the dosimetry probe58 is displayed on the LED display 104. The description of the dosepresent in the eluate at any given time from the start of infusion willbe provided hereafter. The dosimetry controller 62 further comprises apair of LED's 106, 108 which indicate the position of the diverter valve32. Only one of these two LED's 106, 108, should be on at any giventime.

While the normal position of the diverter valve 32 is toward waste,except when eluate is being infused into a patient 56, provision must bemade to clear the tubing 44, 50 of any air prior to infusing a patient56. Accordingly, the dosimetry controller 62 includes a toggle switch110 which is used to hard wire the diverter valve 32 in the patient 56position.

The present preferred embodiment of the invention also includes a set ofthumbwheel switches 112 which are used to set the flow rate which willbe used in internal calculations of dosimetry controller 62. It ispresently anticipated by the inventor that a future version of thepresent invention will include automatic means for determining the flowrate based upon the settings used in the infusion pump controller 60.

Referring now to FIG. 4, a graph of the radioactive dosage present inthe tubing 30 in front of the dosimetry probe 58, is shown. In thegraph, the dosage is measured on the y-axis and time is measured on thex-axis. The time is referenced with zero being the time that thestart/stop inject button 78 on the infusion controller 60 is pushed tocommence infusion.

For approximately 10 seconds there will be no radioactivity present inthe eluate from the strontium-rubidium generator 28. Thereafter, thedose rate rises at a rapid rate up to a maximum, after which the doserate falls to a level value indicative of the steady state regenerationrate of the Sr-Rb generator 28. Thus, when the infusion starts, there isa delay initially as the dose rate builds up, a reduction in dosageafter the generator 28 is partially eluted, and then there is a dosagerepresentative of the steady state regeneration rate of the generator28.

The setting of the dose rate thumbwheel switches 102 tells the dosimetrycontroller 62 at what point along the upward slope of the dosage curveto switch the diverter valve 32 from the waste position to the patient56 position whereby the eluate will be infused into the patient 56. Atthat point the dose indicated by the LED's 100 will start accumulatingfrom zero, where it had been until that point. Similarly, the patient 56volume indicated by the LED's 96 will start to accumulate as of thattime.

Once eluate is infused into the patient 56, it continues to be infuseduntil one of various stop indications occurs. In particular, when thetotal patient 56 dose, set by the thumbwheel switches 98, is reached,the diverter valve 32 is returned to the waste position, and thestepping motor 64 stops, thereby preventing further infusion. Similarly,the diverter valve 32 is switched, and the stepping motor 64 is stoppedwhen the patient 56 volume, preset by the thumbwheel switches 94 reachesits preset value or after the total volume to be eluted, set by thevolume thumbwheel switches 74 reaches its preset value; or when thepurge limit optical stop 68 of the syringe 18 is reached; or if thestart/stop inject button 78 is pushed. Any of the foregoing eventscauses the diverter valve 32 to switch to the waste position, and causesthe stepping motor 64 to stop. Note, however, that the purge and refillswitches 84, 86 are disabled as of the time that the start/stop injectbutton 78 is pushed to commence the infusion.

QUANTIZING RADIOACTIVITY IN A LIQUID STREAM

In order to measure the radioactivity in the saline solution whichpasses through the line 30 in front of the dosimetry probe 58, it isnecessary to count the number of disintigrations which occur in front ofthe probe 58, while at the same time keeping track of the flow rate ofthe saline through the tube 30. Given that these quantities are known,it is possible to measure the total activity in milliCuries (mCi) inaccordance with the followihng formula: ##EQU1## Where, A=total activity(mCi);

C=net counts;

F=flow rate (ml/min);

V=volume in detector view (ml);

E=net efficiency (counts per minute/disintegration per minute);

CM=disintegrations/minute to milliCurie conversion factor; and

Y=net yield of photon.

In the case of the present invention, the above formula can besimplified to: ##EQU2## Where, A=total activity (in milliCuries);

C=net counts (from probe);

F=the flow rate; and

K=the calibration factor.

As noted, the calibration factor, K, takes into account the volume inthe detector's view, the net efficiency of the probe, the conversionfactor in terms of disintigrations per minute to milliCuries, and thenet yield of photons. These factors are substantially constant for anygiven probe and tubing combination for a reasonable amount of time.Accordingly, provision is made on the circuit board to adjust thecalibration factor, K, when the instrument is serviced. However, thecalibration factor, K, is not user adjustable in the normal course ofoperation.

DOSIMETRY PROBE

Referring now to FIG. 5, the dosimetry probe 58 is comprised of aphotomultiplier tube 120, such as the RCA C83009E 14 mm diameter10-stage photomultiplier tube manufactured by the Electro OpticsDivision of RCA Corporation in Lancaster, Pa. The photomultiplier tube120 has a face 122 through which input signals in the form of light arereceived. On the face 122, a plastic scintillator 124, such as a NuclearEnterprises Type 120A manufactured in Edinburgh, Scotland, is mounted.In the preferred embodiment of the invention, the plastic scintillator124 is glued or bonded to the face 122 of the photomultiplier tube 120.After the plastic scintillator 124 has been bonded to the face 122 ofthe photomultiplier tube 120, an aluminum foil covering 121 (shown incross-section) is placed over the face end of the photomultiplier tube120, including the plastic scintillator 124. The purpose of the aluminumfoil covering is to reflect back into the tube 120 any light whichscintillates from the plastic scintillator 124 away from the tube 120.In addition, the aluminum foil covering prevents any stray light whichmight come into the area of the face 122 from getting into the tube 120.Following the application of the aluminum foil, a light tight material,such as black electrical tape 123 (shown in cross-section) is wrappedover the aluminum foil covered tube 120 in order to further prevent anylight from entering into the tube 120. The tape-wrapped tube 120 is theninserted into a mu metal shield 126 which is intended to prevent anyelectromagnetic radiation effects from affecting the output of thedosimetry probe 58. In the preferred embodiment of the invention, thedosimetry probe 58 is plugged into a standard photomultiplier tubesocket base 128 containing a standard resistive biasing network.

DOSIMETRY CIRCUITRY

Referring now to FIG. 6, the photomultiplier tube socket base 128includes a resistive network containing biasing resistors for placingappropriate bias voltages on the ten dynodes in the photomultiplier tube120. Accordingly, the high voltage connection to the photomultipliertube base 128 is automatically biased to provide appropriate operatingvoltages to the photomultiplier tube 120. The high voltage supply 130used in the preferred embodiment of the invention is a 0-1000 volt,adjustable Bertan PMT-10A-P power supply manufactured by BertanAssociates, Inc., Three Aerial Way, Syosset, N.Y. In the presentapplication, the high voltage supply 130 is adjusted to provide anoutput voltage of 950 volts. The photomultiplier tube socket base 128 isan RCA photomultiplier tube socket base, Part No. AJ2273.

An output signal goes from the dosimetry probe 58 on a line 132 to acoupling network comprising a pull up resistor 134, a coupling capacitor136, and a output resistor 138. Accordingly, an AC signal having a peakto peak maximum of approximately 250 millivolts with negative goingpulses, is provided on output line 140.

SINGLE CHANNEL ANALYZER

Referring now to FIG. 7, the schematic diagram for a Single ChannelAnalyzer circuit is shown. The Single Channel Analyzer is used, becausethe pulses on output line 140 from the Dosimetry circuitry are verysharply defined pulses which may occur at very high frequencies. In viewof the fact that it is important to count all the pulses, a very highspeed comparator, such as an AM685 voltage comparator 142, manufacturedby Advanced Micro Devices, 901 Thompson Place, Sunnyvale, Calif., withemitter-coupled logic (ECL) output, or other suitable very high speedcomparator, must be used.

A biasing network 141 consisting of a series of resistors and capacitorsis used as one input to the comparator 142. In view of the fact that thepulses which are handled by the comparator 142 are of very shortduration, a one-shot circuit 144, comprised in the preferred embodimentof the invention, of a Motorola Type 1670 master-slave flip-flopintegrated circuit, is used to stretch the pulse width up to a uniformpulse width of approximately 50 nanoseconds. The output signal from theone-shot 144 is fed into a programmable divide-by-N circuit 146, whichin the preferred embodiment of the invention is comprised of a MotorolaType 10136 universal hexadecimal counter integrated circuit. Thedivide-by-N circuit 146 is programmable. Accordingly, a very high pulserepetition rate coming into the comparator with very short pulse widthsis reformed by the one-shot to have wider, uniform pulses, and the inputsignal is further reformed by the divide-by-N circuit to bring the pulserepetition rate down into any desirable range. In particular, outputs ofthe divide-by-N circuit 146 are provided for N equal to 2, 4, 8, and 16.

Up through this point in the circuit, the devices have all been of ECLtype in order to be able to handle the very high speed pulses which aredetected by the dosimetry probe 58. In view of the fact that it isconventional to use transistor-transistor-logic (TTL) integratedcircuits, a type 10125 ECL-to-TTL level converter circuit 150 is hookedto the output of the divide-by-N circuit 146. Thus, the ECL-to-TTL levelconverter circuit 150 transforms the ECL signal levels into TTL signallevels for further processing. The TTL outputs leave the ECL-to-TTLlevel converter circuit 150 on four lines 152, 154, 156, 158, whichcorrespond to the TTL level of the counts into the Single ChannelAnalyzer divided by 2, 4, 8, and 16, respectively. The counts out on thelines 152-158 will be referred to hereafter as the "net counts".

MULTIPLIER-DIVIDER CIRCUIT

Referring now to FIG. 8, there is a Multiplier-Divider circuit 160 whichconverts the net counts from the Single Channel Analyzer circuit,described above, into a meaningful quantity (milliCuries). TheMultiplier-Divider circuit 160 accepts the "net counts" on an input line162 which is connected to one of the lines 152-158 from the SingleChannel Analyzer (i.e., the raw counts converted into TTL levels andthen divided by 2, 4, 8, or 16) and multiplies them by the eluate FlowRate divided by 100. The result is then divided by a constant, K, inorder to carry out the formula: ##EQU3## Where, A=total activity (inmilliCuries);

N=net counts (from Single Channel Analyzer);

F=Flow Rate; and

K=the calibration factor.

The net counts, N, are first multiplied by a two digit numbercorresponding to the eluate Flow Rate (entered on the Flow Ratethumbwheel switches 112A, 112B, corresponding to the most significantdigit (MSD) and the least significant digit (LSD), respectively, thethumbwheel switches 112A, 112B are on the front panel of the dosimetrycontroller 62, shown in FIG. 3. The multiplication is accomplished bycascading two TTL Synchronous Decade Rate Multiplier circuits (F74167),and sending their outputs through a NAND gate 168. The resulting outputcorresponds to F_(out), where: ##EQU4##

The output pulses are of varying duration, so they are next fed througha pair of one-shots which process them to have a fixed duration. In thepreferred embodiment of the invention, the first one-shot is comprisedof one-half of an SN74123 integrated circuit 170. The first one-shot isnegative edge triggered, and it provides a pulse output of approximately200 nanoseconds. Its output is double buffered through buffers 172, 174into a second one-shot which is comprised of one-half of a CD4098BEintegrated circuit 176 in order to increase the width of the outputpulses, so they will be acceptable to a CMOS divider integrated circuit178. The second one-shot is configured to be leading edge triggered.

The output of the second one-shot is then divided by the calibrationfactor, K, which may have a range of between 3 and 9,999. A CD4059Aintegrated circuit 178 is used as a programmable divide-by-N counter.Programming is accomplished via a series of 16 DIP switches 180 mountedon the printed circuit card. Each set of four switches corresponds tothe BCD settings for 1's, 10's, 100's and 1000's. Pull up resistors (notshown) are employed in the standard manner so that when the DIP switchesare open the inputs to the divide-by-N circuit 178 are pulled high.

The output of the divider 178 has pulses of random widths, so anotherone-shot, made up of the second half of the CD4098BE 176 configured forleading edge triggering, is used. This one-shot provides an output pulseduration of approximately 20 microseconds. Before leaving theMultiplier-Divider circuit 160, the output is double buffered throughbuffers 182, 184 and the output signal on line 186 is sent to the DoseRate circuit. There will be one dose corrected output pulse on line 186for each 0.01 milliCurie of activity which passes by the dosimetry probe58.

DISPLAY CONTROLLER CIRCUIT

Referring now to FIG. 9, the schematic diagram for a Display ControllerCircuit 190 is shown. There are three Display Controller Circuits withinthe dosimetry controller 62. Each Display Controller 190 is used both tointerface a set of thumbwheel switches 192 and to display the quantityassociated with the particular set of thumbwheel switches 192. Thus,there is one Display Controller of 190 for Dose Rate (which works withthumbwheel switches 102 and LEDs 104), one for Patient Volume (whichworks with thumbwheel switches 94 and LEDs 96), and one for Dose (whichworks with thumbwheel switches 98 and LEDs 100). Each Display ControllerCircuit 190 drives four seven-segment displays 194, such as MAN71displays.

The major component of the Display Controller Circuit 190 of thepreferred embodiment of the invention is an Intersil ICM7217IJIintegrated circuit 196, which is a device which provides a directinterface to the seven-segment displays 194. Each Display ControllerCircuit 190 allows the user to set a level, by programming binary codeddecimal (BCD) thumbwheel switches 192. The levels can then be detected.In this way, a preset limit for Dose, for example, will be detected andwill be used to shut down the infusion pump. For Dose Rate, the presetlevel is used to switch the position of the diverter valve 32, throughthe valve driver circuit which will be explained hereinafter. ThePatient Volume can also be preset, and the infusion pump can be stoppedat the preset limit.

DOSE RATE CIRCUIT

The Dose Rate circuit 200, shown in FIG. 10, provides a visual displayof the amount of radiation present in the eluate. The Dose Rate circuit200 employs a Display Controller Circuit, of the type described above.The Dose Rate display is constantly updated to provide the user withDose Rate information. The Dose Rate circuit 200, with the DisplayController, is programmed to set a trigger level for switching theeluate from waste to the patient 56.

The Dose Rate circuit 200 uses signals from the Multiplier-Dividercircuit 160, described above, and from the Control Board which will bedescribed hereinafter. The dose corrected output pulses on line 186 fromthe Multiplier-Divider circuit 160 described above (i.e., 1pulse/0.01/mCi) enter the Dose Rate circuit 200, and are double bufferedby buffers 202, 204. The buffered pulses are then fed through one-halfof a one-shot 206, comprises of a CD4098BE integrated circuit in thepreferred embodiment of the invention. The output from the one-shot 206is gated through NAND gate 207 to the Dose Rate Display 104 since thereare three Display Controller Circuits 190, which are used for Dose(circuit "A"), Dose Rate (circuit "B"), and Patient Volume (circuit"C"), the designation "B10" at the output of NAND gate 207 means pin 10on input connector 197 (see FIG. 9).

The heart of the Dose Rate circuit 200 is an Intersil ICM7207AOscillator Controller integrated circuit 208. This unit, along with adual one-shot comprised of a CD4098BE integrated circuit 210, in thepreferred embodiment of the invention, provides all of the controlnecessary for gating, storing, and resetting the display.

The outputs of the Dose Rate Display Controller Circuit provide an easyinterface to determine when a predetermined count (corresponding to thedose rate which was set on thumbwheel switches 102) has been reached,and to generate a signal which is used for switching the diverter valve32. The valve switching signal is also used to enable the Dose andPatient Volume Displays, 100, 96, respectively.

In the preferred embodiment of the invention, the valve switching signalis derived from one half of a dual D-type flip-flop, such as a CD4013BEintegrated circuit 212. The flip-flop 212 is only enabled during aninjection, i.e., when the infusion pump is being used to either infuseeluate into a patient 56 or to divert it to waste. The enabling "INJECT"signal is generated when the pump is injecting. Once an injection isstarted and a user pre-set Dose Rate limit set on thumbwheel switches102 is met, the flip-flop 212 latches a positive Q output to switch thediverter valve 32 from the waste position to the patient position and toenable the Dose Display and the Patient Volume Display.

CONTROL CIRCUIT

Referring now to FIG. 11, the schematic diagram of the Control circuit220 is shown. The purpose of the Control circuit 220 is to "oversee" allother operations. Specifically, the Control circuit 220 controls theDose Display and Patient Volume Display. The Control circuit 220 alsoprovides timing for resetting the Multiplier-Divider circuit 160, and itbuffers various inputs and outputs to and from the infusion pump controlmodule 60.

The basic function for turning the infusion pump off is the End ofElution signal. The End of Elution signal is derived from either theDose Display 100 or the Patient Volume Display 96. These displays 100,96 are gated to begin counting once the Dose Rate trigger level, the Qoutput from flip-flop 212, reaches its preset limit, as defined by theDose Rate thumbwheel switches 102. Then, once the Dose or Patient Volumeis met, as defined by the Dose thumbwheel switches 98 and by the PatientVolume thumbwheel switches 94, respectively, the Control circuit 220signals the pump to stop.

VALVE DRIVER CIRCUIT

The Valve Driver circuit 230, shown schematically in FIG. 12, is used tocontrol the switching of the diverter valve 32 which directs the eluateeither to the patient 56 or to waste. The Valve Driver circuit 230accepts its input from the Dose Rate circuit or from the Patient LinePurge Switch 110. The Patient Line Purge Switch 110 directly controlsthe valve 32.

The diverter valve 32 is a two position valve which includes electricalswitches which close individually when the valve 32 is fully in eitherthe patient or waste position. Movement of the valve 32 from oneposition to the other is controlled by an AC motor which includes twowindings allowing it to be moved in either direction via an AC motorhaving two windings. When the first winding is energized, the motormoves in a clockwise direction. When the second winding is energized,the motor moves in a counterclockwise direction. At each limit of thevalve movement, there is a microswitch 232, 234 which senses when thevalve limit has been reached.

When one of the microswitches 232, 234 is open, i.e. switch 232, theinput to an associated inverter 236 is essentially at ground. When theswitch 232 closes, the input to the inverter 236 increases toapproximately five volts. After the switch 232 again opens, it takessome time, due to the RC time constant of the associated resistors andcapacitor, before the voltage at the input of the first inverter 236returns to approximately zero. Accordingly, the combination of invertersand the RC network to which each of the switches 232, 234 are connectedacts as a switch debouncer. Thus, the output of inverter 238 will be lowwhen switch 232 is closed and high when switch 232 is opened. Similarly,the output of inverter 240 will be low when switch 234 is closed andhigh when switch 234 is opened.

NAND gate 242 normally has a high output voltage. Accordingly, as willbe obvious to those of ordinary skill in the digital circuitry art, LED106 will be on when switch 232 is closed. Otherwise, LED 106 will beoff. Similarly, LED 108 will be on when switch 234 is closed. Note thatthese LEDs 106, 108 were previously described with reference to thedosimetry controller 62 (See FIG. 3).

When both switches 232, 234 are opened at the same time, there will betwo high signals at the input of NAND gate 254. That will cause NANDgate 256 to trigger a monostable multivibrator comprised of one half ofa CD4098BE integrated circuit 258 which provides a low going outputpulse having a duration of approximately 700 milliseconds in thepreferred embodiment of the invention. The particular time period duringwhich this pulse is low must exceed the time period which it would takefor the diverter valve 32 to be moved from one position to the otherposition. In the preferred embodiment of the invention the movement ofthe diverter valve 32 takes approximately 600 milliseconds. The outputsfrom the monostable multivibrator are fed via EXCLUSIVE OR gate 260 intoa D-type flip-flop 262 comprised of a CD4013BE integrated circuit. Inthe event that the diverter valve 32 did not move from one position tothe other within the prescribed time period, it is presumed that a faultcondition occurred, e.g. the diverter valve 32 jammed. Accordingly, theoperator is advised of the fault condition by both LEDs 106, 108flashing simultaneously. The flashing occurs as a result of the outputof the flip-flop 262 which is connected on line 264 to NAND gate 242being kept high, thereby causing NAND gate 242 to act as an astablemultivibrator which oscillates between high and low outputs therebycausing the EXCLUSIVE OR gates 248, 250 to change states and to flashthe LEDs 106, 108.

At the same time that one output of the flip-flop 262 goes high, theother output, on line 266 goes low. The signal on line 266 is normallyhigh, as it is one input to NAND gate 268. The other input to NAND gate268 is the "End of Elution" signal previously discussed. When bothinputs to NAND gate 268 are high the output on line 270 is high. Theoutput signal on line 270 turns off the infusion pump when it is low.This is the signal which remotely controls the infusion pump, asheretofore described. Thus, in the fault condition, when the signal online 266 goes low the infusion pump is turned off. When there is nofault condition, the infusion pump will be enabled when the End ofElution signal is high.

The Q output from the dose rate circuit 200 enters the Valve ControllerCircuit 230 on line 252. A series of inverters are used to buffer the Qoutput in order to obtain an output on line 254. The output on line 254is used as the input to a pair of solid state relays (not shown) whichselects between the two windings of the motor which drives the divertervalve 32. Thus, when the Q output is high the motor drives the divertervalve 32 into the Patient position, and when the Q output is low, themotor drives the diverter valve 32 into the Waste position.

I claim:
 1. A dosimetry system for a strontium-rubidium generatorcomprising:(a) a photomultiplier tube, having a face through which inputsignals in the form of light are received; (b) a plastic scintillatormounted on said face; (c) means for reflecting back into said tube anylight which scintillates from the plastic scintillator; (d) means forpreventing stray light from striking said plastic scintillator; and (e)a single channel analyzer electrically connected to said photomultiplertube for receiving pulses from said photomultiplier tube, said singlechannel analyzer comprising a very high speed comparator which receivesinput pulses from said photomultipler tube including means for analyzinginput pulses having pulse widths of significantly less than 50nanoseconds.
 2. The dosimetry system of claim 1 further comprising meansfor reducing the pulse repetition rate of said input pulses.
 3. Thedosimetry system of claim 2 wherein said means for reducing the pulserepetition rate of said input pulses comprises a programmabledivide-by-N circuit capable of receiving a very high pulse repetitionrate and bringing the pulse repetition rate down into any desirablerange.
 4. The dosimetry system of claim 3 wherein said means foranalyzing input pulses having pulse widths of significantly less than 50nanoseconds is comprised of a one-shot circuit.
 5. The dosimetry systemof claim 4 wherein said one-shot circuit is comprised of an emittercoupled logic flip-flop which can accept input pulses having pulsewidths of significantly less than 50 nanoseconds.
 6. The dosimetrysystem of claim 1 wherein said means for analyzing generates an outputcomprising output pulses and further comprising means for converting theoutput pulses of said means for analyzing into a measure ofradioactivity.
 7. The dosimetry system of claim 6 wherein said means forconverting the output pulses into a measure of radioactivity comprises aMultiplier-Divider circuit which accepts said output pulses andmultiplies them by a number corresponding to the eluate Flow Ratedivided by a constant, K, in order to carry out the formula: ##EQU5##Where, A=total acitvity (in milliCuries);N=net counts (from SingleChannel Analyzer); F=Flow Rate; and K=the calibration factor.